1. Field of the Invention
The present invention relates to technology for attaching a heat radiator or the like to a package substrate.
2. Description of the Related Art
Various types of semiconductor chips, such as a CPU (Central Processing Unit) and a DSP (Digital Signal Processor), which controls electronic equipments, are constructed of various electronic components including active elements, such as transistors and passive elements, such as capacitors. Part of electric energy for driving these electronic components is converted into thermal energy and dissipated as heat. The performance of the electronic components typically has temperature dependence. Then, the dissipated heat has an inverse effect on the performance of the electronic components, and by extension that of the semiconductor chips. Thus, technologies for cooling the semiconductor chips are of significant importance in controlling the electronic devices properly.
To cool the semiconductor chips, some conventional arts provide a heat radiator, such as a heat sink on the semiconductor chip, which is disclosed in Japanese Patent Laid-Open No. 8-46100. Heat emitted from the semiconductor chip is transferred to the heat radiator, and the heat is dissipated from the heat exchange surface of the heat radiator. Typically, the heat radiator is designed to have large heat exchange surface so as to transfer the heat from the semiconductor chip to cool fluid or gas surrounding the semiconductor chip efficiently. In order to cool the semiconductor chip regularly, it is necessary to equalize the heat resistance between the heat radiator and the semiconductor chip by pressurizing the heat radiator against the semiconductor chip.
In the conventional art, a back plate is attached on a back side of the package substrate to prevent deformation of the package substrate, thereby equalizing the heat resistance between the heat radiator and the semiconductor chip. Thus, stable cooling with the heat radiator is realized. However, this method increases the number of components and tasks for assembling the semiconductor device. Furthermore, increasing the area of the heat exchange face of the heat radiator makes the attachment of the heat radiator on the package substrate more difficult.